Method of operating open hearth furnaces



Jan. 9, 1934.

A. J. BOYNTON 1,942,682 METHOD OF OPERATING OPEN HEARTH FURNACES Filed Sept. 28, 1951 3 Sheets-Sheet l drfizarJ. Beg/722 0 Jan. 9, 1934. A. J BQYNTQN 1,942,682

METHOD OF OPERATING OPEN HEARTH FURNACES g g g Fatentetl 3. 9,, 1934 STATES t at PATENT OFFIC' mesne assignments, to tion Company, Chioag Delaware Arthur .7. Boynton, Chicago, 111., assignor, by

Open Hearth Combuso, 111., a corporation of Application September 28, 1931 Serial No Claims. (Cl. 263-) This invention relates to a new and improved method for the operation of open hearth furnaces and other furnaces of the same general character and to furnaces and controls adapted to carry out the improved method of operation.

At the present time it is a practically universal custom in the operation of the open hearth furnace to admit fuel through a single gas port lying along the longitudinal. vertical axis of the furnace and air through a single air port lying above the gas port and wider than the latter. There are some variations from this construction but all existing arrangements discharge the gas into the furnace in such a way that the gas stream is surrounded above and on either side by a stream of air. Combustion takes place along the surfaces of contact between the gas and air. If the two streams are nearly parallel the mixture of the stream a minimum, the combustion is slow, the flame is long, and the temperature resulting from the combustion is low by comparison with maximum temperature obtainable.

Control of the length and intensity of flame is obtained by varying the shape and size of the ports and of the furnace ends, so as to affect the rate of mixture of the gas with the air. These variations make possible to some extent the influencing of the length and intensity of flame. Such means of control are determined by practical experience under a constant set of conditions, and are not correctly applicable to different rates of use of fuel in the same furnace, and still less to different fuels in different furnaces.

In all open hearth furnace practice a large excess of air beyond that required for combustion of the fuel is present. This excess is necessary with the present type of furnace in order to protect the roof from fusion and consequent destruction. The heat of the open hearth flame is so intense that the roof is made several feet higher than is required for the passage of the flame, and the space corresponding to this excess height of roof is preferably kept full of air with as little mixture with fuel gases or products of combustion as is possible. This condition is described as keeping the flame low, or making the flame hug the bath".

Admission of gas to the open hearth furnace is under premure from a producer or holder.

This pressure, together with the height of the furnace above the reg'enerators gives a jet effect to the gas which is purposely'increased by re-- duction in area of the gas port and by shaping it so as to serve as a nozzle. The gas therefore enters the furnace with considerable velocity.

The air may enter the furnace either under natural draft or under pressure. In either case the velocity imparted to the air stream is common and practically the same in every part. The result of this single admission of air is that the air which combines with the fuel has nearly the same velocity as that which flows throughthe furnace close to the roof. The functions of these two parts of the air stream are separate and distinct. The lower part of the stream unites with so the fuel while the upper part acts as a preventive of flame contact with the roof. It is advisable that the velocity of that part of the air stream which furnishes air for combustion should substantially coincide in velocity with the gas stream while the velocity of the upper part of the air stream should be governed by the temperature to which it is raised by radiation of heat from the flame.

The effect of such an equality of velocityhetween gas and air for combustion is a lack of turbulence which is favorable to keeping the flame low and preventing its dissipation throughout the whole of the outgoing end of the furnace.

This condition of equality of velocity between gas and air for combustionis an ideal one for maintaining a steady flame. There are, however, difl'erences in furnace conditions which require different flame conditions for best results. when melting scrap in front of the port a short, intensely hot flame is desirable, a flame which can best be produced by rapid admixture with the gas of the entire quantity of air required for combustion. At other times a longer, less oxidizing flame is required.

The intensity and temperature of the flame depend upon the extent to which mixture has taken place at the moment of ignition. Complete mixture, together with air in exactly the correct proportion causes maximum temperature and minimum length of flame. With natural gas a mixture of ten parts of air and one part of gas by volume will create a short flame which will have an intensive melting power ately in front of the port. If the gas and air leave the port unmixed, the maximum r ture will be much less and the flame will be correspondingly longer.

A. second consideration is the jetting sheet from the port which causes a rapid travel of flame across the bath. This rapidity of travel is favorable to heat transfer. At the same time the flame should be kept low, partly because a flame at a considerable distance from the bath proximately eight times that of natural gas and four times that of coke gas for the same quantity of heat. A jet eflect which is ample for producer gas is therefore deficient for other gases excepting as the latter are mixed with primary Protection of the roof is efiected by excess air brought in from the air port which surrounds the flame above and at the sides, and also protects the back and front walls. The speed of this blanket of excess air is not material, provided it is rapid enough to maintain the temperature of the air.

The pressure of gases in an open hearth furnace should be as nearly neutral as possible, when measured at the floor plate. There will be some positive pressure at the roof, due to height of column of hot gases. There will be a slight pressure at the ingoing end and a slight draft at the outgoing end. If these conditions are fulfilled there will be a minimum indraft of cold air, which tends to chill the furnace and the regenerators, and the path of the flames will be free from disturbance due to varying pressure.

It is an object of the present invention to provide a new and improved method of furnace operation.

It is a further object to provide a new and improved furnace and accessories for carrying out my improved method.

It is an additional object to provide a method -of furnace operation adapted to provide the which avoids the possibility of the absorption of sulphur by the metallic charge by prompt conversion of Has to water vapor and sulphur dioxide, in which form the sulphur is not absorbed.

It is also an object to provide a method which aflords protection for the furnace roof and which minimizm the flow'of gases through the furnace, l0 as to reduce the carrying over of molten slag and slag vapors into the checkers and the erosion of the furnace ports thereby adding materially to the life of the furnace brick work and decreasing the cost of repairs.

Other and further objects will appear as the description proceeds.

1 have shown certain preferred embodiments of my invention in the accompanying drawings, in which- Figure l is a somewhat diagrammatic layout of my invention applied to an open hearth furnace of the type using non-regenerated fuel gases;

Figure 2 is a view similar to Figure 1 showing the invention applied to the type of furnace in which the gaseous fuel is regenerated; and

Figure 3 is a plan view of the furnace structure shown in Figure 2.

Referring first to the form of construction shown in Figure 1, the open hearth furnace comprises a hearth 11 having a roof 12, and a fuel port 13. The uptake 14 leads to the fuel port 13 and is closed at its upper end by the mushroom valve 15 which may be raised or lowered by means of the valve stem 16. The air port 17 is located above the gas port 13 and is in communication with the uptake 14 when the valve 15 is raised. The uptake 14 communicates with the slag pocket 18 which in turn communicates with usual types of regenerators. The uptakes 19 lead to the upper air port 1'7 and communicate at their lower ends with the slag pocket 20, which is connected to the usual type of regenerators.

The regeneretors, which are not shown, are connected throughpassages to the passage 21 which leads to the stack 22. It will be understood that the furnace is of the reversible type and that only one end of the furnace is shown in Figure 1. The passage 21 will be connected to regenerators at both ends of the furnace, this connection being governed by reversing valves so that the passage is in communication with only one end of the furnace at a time.

The fuel burner 23 is inserted through the end wall 24 of the furnace across the uptake 14 and down into the fuelport 13. This burner 23 is provided with connections 25 and 26 for water cooling, and with a gas connection 2'7 which is controlled by a valve 28. A calibrated orifice 2915 located in the gas connection adjacent the burner 23 and a pressure communicating pipe 30 extends into the pipe 2'7 on the incoming side of the orifice 29. This pipe is connected through pipe 31 with the fuel volume indicator 32. Pipe 30 is also connected through pipe 33' with the chamber 34 which is located on one side of the diaphragm The pressure transmitting pipe 36 communicates with the pipe 2'7 on the outlet side of the orifice 29 and this pipe 36 is connected with the fuel volume indicator 32 by pipe 3'7. The pressure pipe 36 is also connected through pipe 38 with the chamber 39, which is located on the opposite side of diaphragm to the chamber 34.

The air for combustion which passes into the furnace through the slag pocket 18 and uptake 14 is introduced through the passage 40. The entrance end of this passage 40 is provided with the plate 41 having a calibrated orifice therein. This passage 40 is shown as provided with a power driven fan 42 for producing a forced draft.

The passage of air from the passage 40 into the regenerator, and thus into the furnace, is controlled by valve 43 which is operated through link 44 and the piston rod 45 which is driven by piston 46 in cylinder 4'7. The pressure tube 48 connects with passage 40 outside of the plate 41 and this pipe 48 is connected by means of pipe 49 with the air volume indicator 50. Pipe 48 is also connected through pipe 51 with the chamber 52 located adjacent the diaphragm 53. The pressure pipe-54 communicates with the passage 40 upon the inner side of the plate 41 and communicates with the air volume indicator through pipe 55. Pipe 54 also communicates through pipe 56 with the chamber 5'7 located on the opposite side of diaphragm 53 to the chamber 52.

The draft ratio control apparatus 58 comprises an arm 59 which is engaged by the thrust rod 60 which is carried and moved by the diaphragm 35. This arm 59 engages a thrust-transmitting member 61 which may be moved into and out of the control apparatus by means of the adjusting handwheel 62. The member 61- also engages the power nozzle 63 which is pivotally supported at 64 and supplied with a flow of fluid under pressure through pipe 85. The other side of the nozzle 63 is engaged by the thrust-transmitting member 66 carried by the diaphragm 53.

The adjacent passages 67 and 68 are located opposite the discharge end of the nozzle-63. The passage 68 leads to the chamber 69 to the left of the piston 46 in the cylinder 47, and the passage 67 leads to the chamber 70 on the right side of the piston 46 in cylinder 47.

The pipe 71 leads into the top of the furnace and communicates through pipe 72 with the furnace pressure indicator 73. This pipe 71 also communicates through pipe 74 with the chamber 76 located on one side of the diaphragm 76. The chamber 77 on the opposite side of diaphragm 76 communicates with the atmosphere. The pressure transmitting arm 78 is carried by diaphragm 76 and engages the swinging nozzle 79. nozzle is provided with a supply of fluid under pressure through pipe 80. The spring 81 engages the opposite side of nozzle 79 and the tension of the spring may be regulated by means of the knob 82. The nozzle 79 is adapted to discharge fluid against a slide 83 which controls the flow of fluid under pressure from the pipe 84 and distributes that flow between the pipe 85 and pipe 86. The pipe 85 leads to the upper side of the cylinder 87 and the pipe 86 leads to the lower side of cylinder 87.

Cylinder 87 contains a piston 88 and a piston rod 89 which rod carries a pulley 90 fltted into a blght of the cable 91. One end of the cable 91 is fixedly secured at 92 while the other end of the cable passes over the pulleys 93 and 94 and connects to the damper 95 which is enclosed in the housing 96 and slides on guides 97in thepassage 21 leading to the stack.

Referring now to the form of construction shown in Figures 2 and 3, a furnace chamber- 100 is shown as provided with a roof 101, the gas port 102, and the air port 103 located above the gas port. The gas passage 104 leads to the gas checker 105, and from the checker to This wardly through the uptake 114 into the rear The furnace pressure pipe 121 is connectedby pipe 122 to the furnace pressure indicator 123. The pipe 121 is also connected by meansof pipe 124 to the stack damper control device l25-which is similar in construction to that "described in connection with Figure 1 and need not be described in detail. This control 125 operates the damper 126, which is located in passage l27 leading to the stack 128. The pricontrol damper 111 is operated by --means of the cylinder 129 and piston rod 130.

The movement of the piston in cylinder 129 is controlled .by fluid under pressure flowing through pipes 131 and 132 from the control device 133-which is similar to the corresponding control device shown in Figure 1, and which need not therefore be described in detail.

The volume of incoming gas which comes through passage 104 is measured by means of the orifice in the plate 134 and the volume is shown on the gas volume indicator 135. This gas volume is also transmitted to one side of the control device 133. The air volume is transmitted to the air volume indicator 136 through pipes 137 and 138, which connect to the primary air intake passage 108 on either side. of the plate 110. This air volume is transmitted to the opposite side of the control device 133.

In operating these types of furnace to carry out my invention, and referring first to the form of construction shown in Figure 1, the gaseous fuel is introduced through nozzle 23 which extends into the gas port 13. At this time the damper 15 is in the lower position, as shown in Figure 1. The volume of this fuel is indicated on the indicator 32 and this volume aifects the diaphragm 35. The volume of air entering the primary air regenerator, and thus the volume a greater portion of its fluid flow into the pipe 8 68. This fluid will operate upon the left side of the piston 46, drawing the piston rod 45 inwardly and opening the air valve 43. This increases the volume of air to the proper amount so as to maintain the proper proportion with the increased fuel gas. When the pressures are again balanced the nozzle 83 will be restored to its neutral position. Y

The flow of air through the gas slag pocket 20 and the upper air port 17 is controlled by means of varying the stack draft. This air is not under forced draft and is drawn through the furnace by the stack draft. The pressure in the upper portion of the central part of the furnace is shown on indicator 73 and this pressure controls the diaphragms 76 which, in turn, through nozzle 79 controls the flow of fluid under pressure through pipes 85 and 86. Thus ifthe pressure in the furnace builds up, the

nozzle 79 will be thrust to the left, a greater fiuid'flow will pass through pipe 85, and the piston 88 will be lowered to raise the damper 95 and thus increase the stack draft and reduce the furnace pressure.

The operation of the form of. construction shown in Figures 2 and 3 is quite similar to that just described. The furnace pressure is maintained in the same manner by means of control of the stack draft through raising and lowering the @damper in the passage 127 leading to the stack. In this case the gas is under lower pressure as it is regenerated, but the gas volume and air volume are measured and their combined effect on the control device 133 serves to operate the damper 111 controlling the incoming primary air so as to maintain the amount of that air in the proper ratio to the amount of incoming It will be understood that the damper 15 in raised on the outgoing end of the furnace in order to permit a greater quantity of the products of combustion to pass down into the regenerators for the primary air.

While types of open hearth furnaces have been shown and described, it will be understood that my invention is also applicable to other types of heating furnaces, soaking pits, and the like, and the term open hearth furnace in the claims isto be interpreted as covering other furnaces of this general character. The specific furnaces and specific control devices shown are to be understood to be illustrative only as I contemplate such changes and modifications as come within the spirit and scope of the appended claims.

I claim:

-1. The method of open hearth furnace operation, which comprises introducing a controlled quantity of fuel, a controlled quantity of primary mitted, controlling the volume of primary air to maintain a predetermined ratio with the gas, and admitting a separate stream of secondary air under induced draft from a separate source.

4. The method of open hearth furnace operation, which comprises introducing a stream of gas. measuring the volume of gas, introducing a controlled volume of primary air, controlling the volume of primary air automatically by means dependent upon the volume of gas, and admitting a separate stream of ,s'econdary air from a separate source.

5. The method of open hearth furnace operation, which comprises introducing a stream of gas, measuring the volume of gas, introducing a controlled volume of primary air, controlling the volume of primary air automatically by means dependent upon the volume of gas, admitting a separate stream of secondary air, measuring the furnace pressure, and automatically controlling the stack draft by the furnace pressure.

6. In an open hearth furnace, a combined fuel and air port, means for leading fuel to said port, an air uptake leading to said port, an air regener- 1,942,682 'Figureiandthedamper11linFigure2are ator leading to said uptake, means for forcing air under pressure to said regenerator, a air port, an air uptake leading to said port, a separate air regenerator for said secondary air and a separate connection to the air for said separate air regenerator.

7. In an open hearth furnace, a combined fuel and air port, a passage leading fuel to said port, a passage leading air to said port, means for measuring the volumes of air and fuel passing to said port, automatic means controlled by the volumes of air and fuel for maintaining a predetermined ratio between said volumes, a secondary air port, and means for leading a separate stream of air to said port from a source independent of said first-named air port.

8. In an open hearth furnace, a combined fuel and air port, a passage leading fuel to said port, a passage leading air to said port, adamper in said latter passage, means for measuring the volumes of air and fuel passing to said port, automatic means controlled by the volumes .of air and fuel for operating said damper to maintain a predetermined ratio between said volumes, a secondary air port, and means for leading a separate stream of air to said port from a source independent of said first-named air port.

9. In an open hearth furnace, a combined fuel and air port, a passage leading fuel to said port,

a passage leading air to said port, means for measuring the volumes of air and fuel passing to said port, automatic means controlled by the volumes of air and fuel for maintaining a predetermined ratio between said volumes, a secondary air port, means for leading a separate stream of air to said port, means for measuring the pressure in said furnace, a stack, a damper controlling flow from the furnace to the stack, and means controlled by the furnace pressure for operating said damper to maintain a predetermined pressure in said furnace chamber.

10. In an open hearth furnace, a combined air and gas port, air and gas regenerators and passages connecting the regenerators and combined port, means for measuring the gas volume passing to said port, a fan for forcing air to said ort, a.- damper for controlling the flow of air s the port, a control for-the damper operated by the gas and air volumes to maintain a predetermined ratio between said volumes, a secondary air port, a separate secondary air regenerator, separate passages connecting the secondary air regenerator and secondary air port, means for measuring the furnace pressure, a damper controlling the stack draft on the furnace, and means regulated by the furnace pressure for operating the damper.

ARTHUR J. BOYNTON. 

